https://www.torahmusings.com/2022/04/contemporary-tzaraat-2/
The question why we don’t observe the laws of metzora has troubled many Torah scholars. In his introduction to his Tiferet Yisrael commentary on Mishnah Nega’im, R. Yisrael Lipschitz recalls that in his youth he asked the great R. Akiva Eiger this question. He responded that he himself was wondering the same thing for a long time and does not have a good answer. [18] R. Lipschitz himself answers along the lines of Rambam. Whereas Rambam stressed the need for a kohen meyuchas in determining a metzora to be impure, R. Lipschitz claimed it was essential for the purification process. Because the purification process included shaving the head, it could only be done if the metzora was really impure and had now been cured. But since a metzora can only become impure by the pronouncement of a real kohen, if it turned out the kohen was not a valid kohen, the shaving of the head would be a Torah violation. [19]